Railcars are often subjected to low speed collisions experienced during operation of a train which can involve pulling, pushing, stopping or coupling railcars for example. Because of the significant mass that railcars possess, such collisions can result in damage not only to the railcars but also to the cargo they carry. For this reason, railcars are fitted with an end-of-car system to provide shock absorption and diminish the impact that low speed collisions might have on a railcar and/or its contents.
Two types of end-of-car energy management systems are currently being used in the industry: buffers (also called end-of-car cushion systems) and draft gears. Both buffers and draft gears provide shock absorption, however buffers use a fluid as a damping medium while draft gears are mechanical devices. Typically, a draft gear uses a spring-loaded mechanism where damping is achieved via friction. Examples of draft gears can be found in U.S. Pat. No. 8,870,002 and U.S. Pat. No. 8,939,300. The stroke length of buffers is generally significantly bigger than the stroke length of a draft gear and thus they typically provide better impact protection in buff (compression). However, a disadvantage of buffers is that they need regular maintenance and inspection in order to ensure that no leaks are present. Failure to do so may result in buffer malfunction and thus a possible accident. Moreover, regulations regarding the maintenance of buffers are stringent and if not followed can result in significant penalties to the railway operator.
Moreover, buffers are designed such that they cannot provide protection against draft forces. They only operate in a buff direction. As a result, the knuckles that connect railcars to each other experience severe stresses when a car is being pulled, such as when the train accelerates. Knuckle breakage is not uncommon on railcars using buffers for energy management.
End of car energy management systems that provide draft protection exist. Those systems are designed on the principle that the longer the draft stroke the better the performance. However, long draft strokes have an unintended disadvantage, which is the build up of slack between the railcars that needs to be factored in the design and the installation of the pneumatic hose connections that run from one railcar to the other. To accommodate the slack, a sufficient excess of pneumatic hose length must be provided to avoid over stretching the hose when the energy management system is fully extended. The excess hose length may become so long that the hoses may drag on the ground when an energy management system is in a neutral operating position. To avoid that issue, a support system for the hoses is required, which is costly to procure, install and maintain.
Draft gears generally have a short stroke length and therefore do not provide comparable impact protection to buffers, however draft gears are not subject to leaks since they don't use hydraulic components and thus are inherently more reliable.